How to change tax code in Credit Transactions

 Hello,

For Canadian transactions, we have tax codes of GSTPST, GST and PST.  When creating tax credits from the transactions via Actions - Credit (same as Credit Transactions form), when I click on credit lines, I cannot override the tax code.  I have changed the profile option Tax: Allow Override of Tax Code to Yes for the responsibility I am in, however I still cannot change the tax code when crediting an existing transaction.  Is there a way to do this?  We are on 11.5.10.2.

Please advise,

Thanks

Mandy